This invention relates to a blast furnace stove, although equally applicable to stoves for other purposes, of the type having a combustion chamber coupled to a burner to supply hot products of combustion to a checker-filled heat exchanger for heating an air supply. More particularly, the present invention relates to an apparatus and method of operating such a stove wherein the combustion chamber includes a mixing bed comprised of a multitude of bodies of high-temperature material on a support to mix and heat fuel and air supplies for combustion thereabove in the combustion chamber.
As is well known in the art, a plurality of blast furnace stoves is operated at time-displaced cycles to heat a blast of air used to provide heat for a blast furnace. In each stove there is a vertical combustion chamber coupled to a burner to inject gas, usually blast furnace gas, and air into the bottom portion of the chamber for combustion. The combustion products are directed by a dome from the top of the combustion chamber into a regenerator through passageways in a filling of checkerbrick to heat the blast of air. The blast of air usually flows through the openings in the checkerbrick countercurrent to the flow of combustion gases. Generally, the heated air is withdrawn through an opening in the side wall of the combustion chamber. In such a blast furnace stove, the burner is usually arranged to direct the flame horizontally into the bottom of the vertically-extending combustion chamber. A water-cooled burner valve opens and closes the passageway from the stove gas burner into the combustion chamber and provides thermal protection for the metal parts of the burner. The stove is generally comprised of a metal shell used to support a lining of refractory material. An internal refractory wall that includes a breast wall is joined to the lining of refractory material within the metal shell to form part of the actual combustion chamber and provides support for the checkerbrick in the heat-storage chamber or regenerator. More than one lining of refractory material may be used in the combustion chamber to withstand the high temperature developed therein.
The present invention is addressed to overcoming certain disadvantages to the construction and operation of known forms of blast furnace stoves. Thus, for example, the life of the refractory material is reduced in the combustion chamber at the site where the burner flame or admixed fuel and air fed from the burner impinges on the refractory wall. Repairs to the refractory material at this area and elsewhere can be usually carried out only after the stove is cooled to near ambient temperature. This requires a long interruption to the operation of the stove which seriously affects its economical operation. Moreover, direct flame impingement on the refractory of the combustion chamber brings about the development of large thermal stresses in the metal shell of the blast furnace stove. These stresses increase the need for refractory maintenance since they tend to separate the shell from the refractory, whereby voids may occur that permit hot gas to contact the shell which worsens with each cycle of operation. When a metallic burner housing is used, it must be joined by a rigid and close-coupled connection pipe that is vital and has uncompromising importance. This requires a water-cooled valve to isolate the burner from the combustion chamber. The valve is subject to mechanical failure and it is cumbersome, but nevertheless essential in most blast furnace stoves to isolate the burner from the combustion chamber, particularly during the time when the blast of air is fed into the stove for heating. The wall opening in the refractory for the fuel and air from the burner is normally situated below the opening in the combustion chamber used to discharge the blast of heated air from the stove. During this period of stove operation, radiant heating occurs in the combustion chamber which places stringent requirements for thermal isolation of the burner from the combustion chamber. A water-cooled valve is also necessary to isolate the burner from the combustion chamber because of the pressure of the blast air which is typically between 30 and 50 psig.
In a further aspect, when an external burner is used for a blast furnace stove, the burner structure forms a space where dangerous quantities of fuel gas may collect should a leakage occur in a gas shutoff valve. Such a gas leak is not an uncommon occurrence and it permits an accumulation of gas that may extend into the burner combustion air-supply pipe for the burner and the air blower. The gas can pass in this manner to the surrounding outside area and, therefore, presents a hazard to operating personnel due to gas inhalation, fire and explosion.
In U.S. Pat. No. 3,779,690, there is disclosed a gaseous mixing device for a blast furnace stove to meet the need for a higher temperature air blast (1200.degree. C. to 1300.degree. C.) in which a refractory burner is used in a combustion chamber. The mixing device is designed from refractory material to form a horizontal chamber arranged to impart a swirling or rotational movement to mix air and combustible gas at the bottom of the combustion chamber. Channels tangentially intersect with a mixing chamber having a conical throat at its upper end to move the gases inwardly toward the center for combustion above the throat in the combustion chamber. This system, while eliminating the traditional metallic burner, places stringent requirements for the refractory material in the stove. Particulate material carried with the fuel and air supply has a detrimental effect on the refractory material which can pass into the checkerbrick in the heat-storage chamber and reduce the gas flow space, thereby increasing the pressure drop. Moreover, the refractory material forming the mixing device is subject to severe radiant heating during an air-heating cycle of operation. The present invention is addressed to an improved construction and method of operating a blast furnace stove. It includes a mixing bed in a combustion chamber thereof to mix and heat fuel and air supplies for combustion thereabove.